Miyazaki begins the film with a clear warning about marine pollution, depicting the sea and coastline littered with rubbish. Also notable is the portrayal of Sosuke's mother, Lisa; her frustration when she is late for work, and when her husband is late home, is surprisingly realistic, given the otherwise innocent nature of the film.
As in many of Miyazaki's films, there are magical elements which are never fully explained. Ponyo's father, for example, is a kind of Captain Nemo figure, a wizard who lives underwater; her mother is a sea goddess. At the end of the film, the wizard appears to rejuvenate a group of elderly people in a magical water-bubble, in an odd and surely unintentional echo of the film Cocoon.